Demo Docker Commands

Welcome to this comprehensive guide on essential Docker commands. In this article, you’ll learn how to run containers, list and remove them, manage images, and pull images from Docker Hub. If you are new to Docker, check out the official Docker documentation for further reading.

Running Containers with Docker

The Docker run command is used to start a container from a specified image. Below is an example of starting a container:

root@Docker:/root # docker run

To explore a variety of available images, visit the Docker Hub website and click on "Explore". Here, you'll find many official images such as "hello-world", CentOS, Ubuntu, and more.

For instance, to run a CentOS container, use:

root@Docker:/root # docker run centos
Unable to find image 'centos:latest' locally
latest: Pulling from library/centos
74f0853ba93b: Downloading [===============>                ] 13.52MB/72.25MB

If you have custom images, use the format "username/repository". For example, if your Docker Hub ID is "Mumshad" and you have an image named "ansible-playbook", reference it as "Mumshad/ansible-playbook".

Below is another simulated output showing Docker downloading the image:

root@Docker:/root # docker run centos
Unable to find image 'centos:latest' locally
latest: Pulling from library/centos
74f0853ba93b: Downloading [==================>              ] 49.2MB/72.25MB

You can explicitly download an image using:

docker pull centos

root@Docker:/root # docker run -it centos bash

Once inside the container, you can verify the OS by checking the release information:

root@0aelec7e1d3 /# cat /etc/*release*
CentOS Linux release 7.3.1611 (Core)
Derived from Red Hat Enterprise Linux 7.3 (Source)
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

After verifying, simply exit the container.

Listing Running and Exited Containers

To list currently running containers, execute:

root@Docker:/root # docker ps

If your interactive CentOS container exited after the session ended, it will not appear in the above list. To view all containers, including those that have exited, use the -a flag:

docker ps -a

For example, after starting a CentOS container with a sleep command:

root@Docker:/root # docker run centos sleep 20

You can run this command in the background using the -d flag:

root@Docker:/root # docker run -d centos sleep 20

Now, view the list of running containers:

root@Docker:/root # docker ps
CONTAINER ID        IMAGE     COMMAND      CREATED         STATUS         PORTS               NAMES
62bbd3c98f08        centos    "sleep 20"   7 seconds ago   Up 6 seconds                       flamboyant_noyce

Since the container will exit after the sleep duration, re-checking with docker ps later will show that it has stopped. To confirm the status of all containers, including exited ones, run:

docker ps -a

Containers will display exit codes indicating their termination status (e.g., 0 for normal exit, 137 for forceful termination).

Removing Containers

Cleanup unused containers using the docker rm command. You can remove a container by its specific ID or name.

To remove a container with a specific ID:

docker rm 1619625d7f5a

You can also remove multiple containers by providing parts of their IDs or names:

docker rm 345 e0a 773

Below is a sample session demonstrating container removal:

root@Docker:/root # docker rm nervous_tesla
root@Docker:/root # docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                   PORTS               NAMES
5d5b09577c30        centos              "sleep 2000"       2 minutes ago      Exited (137) About a minute ago                     sere
62bbd3c98f08        centos              "sleep 20"        5 minutes ago      Exited (0) 5 minutes ago                       flam
root@Docker:/root # docker rm 345 e0a 773
345
e0a
773
root@Docker:/root # docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                   PORTS               NAMES
5d5b09577c30        centos              "sleep 2000"       2 minutes ago      Exited (137) About a minute ago                     sere
62bbd3c98f08        centos              "sleep 20"        5 minutes ago      Exited (0) 5 minutes ago                       flam

Managing Docker Images

Throughout your Docker sessions, you might have pulled several images such as hello-world, ubuntu, and centos. To list all locally available images, run:

root@Docker:/root # docker images
REPOSITORY   TAG       IMAGE ID       CREATED                  SIZE
busybox      latest    d20ae45477cb   Less than a second ago   1.13MB
ubuntu       latest    ccc7a11d65b1   9 days ago               120MB
centos       latest    328edc84f1b    2 weeks ago              193MB
hello-world  latest    1815c82652c0   2 months ago             1.84kB

To remove an image, use the docker rmi command. For example, remove the busybox image with:

root@Docker:/root # docker rmi busybox
Untagged: busybox:d20a45477cbc98f3f111d0cdff28ef406ce2e2020ef971b14e4efc0
Deleted: sha256:b82b57400c1cab8235962c07f81084ecd32fd25807207b99f52a3cb8692
Deleted: sha256:26742d9d02d698f5696ca4dc4cbe87145d47e3bf6feea4025ab28f240f2

Similarly, remove the Ubuntu image with:

root@Docker:/root # docker rmi ubuntu
Untagged: ubuntu:latest
Untagged: ubuntu@sha256:344714871495f9e84096d37580d12b0e67b1a77fd6155ce001edad
Deleted: sha256:ccc7a1d65b1785dab6a1c0c70119675476943d9cc95fae798
...

To remove a CentOS image used by a container, first delete all associated containers and then run:

root@Docker:/root # docker rmi centos
Untagged: centos:latest
Untagged: centos@sha256:b362758f4793674edb79ec5c7192074b2eacf200c006e127069856484526ccf2
Deleted: sha256:b362758f4793674edb79ec5c7192074b2eacf200c006e127069856484526ccf2

After cleanup, you might only be left with the "centos" and "hello-world" images, which you can remove in a similar manner.

Pulling Docker Images

While the Docker run command pulls missing images automatically, you can download an image without starting a container using the docker pull command. For example, to pull the Ubuntu image, run:

root@Docker:/root# docker pull ubuntu
Using default tag: latest
latest: Pulling from library/ubuntu
d5c6f90da05d: Downloading [==========================>]
1300883d87d5: Download complete
c220aa3cfc1b: Download complete
2e9398f099dc: Download complete
dc27a084064f: Download complete

After pulling the image, verify its presence:

root@Docker:/root# docker images
REPOSITORY   TAG       IMAGE ID       CREATED         SIZE
ubuntu       latest    ccc7a11d65b1   9 days ago      120MB

Running Containers in Detached Mode and Executing Commands

To run containers in the background, use the -d (detached) flag. For instance, to run an Ubuntu container that sleeps for 100 seconds:

root@Docker:/root # docker run -d ubuntu sleep 100

Then, check the container’s status with:

root@Docker:/root # docker ps
CONTAINER ID        IMAGE     COMMAND       CREATED         STATUS         PORTS               NAMES
cla19d3a7ca70        ubuntu    "sleep 100"   7 seconds ago   Up 6 seconds                       suspicious_neumann

To execute commands on a running container, use docker exec. For example, viewing the OS release information inside the Ubuntu container:

root@Docker:/root # docker exec c1a9d3a7ca7 cat /etc/*release*
NAME="Ubuntu"
VERSION="16.04.3 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.3 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial

Conclusion

In this guide, we explored basic Docker commands that help you run containers both interactively and in detached mode, list running and stopped containers, remove containers and images, and pull images from Docker Hub. Experiment with these commands to enhance your Docker skills and master container management.

For more detailed technical resources, consider these references:

• Kubernetes Basics
• Docker Hub
• Terraform Registry

Happy Dockering and see you in the next article!